1. Field of the Invention
The present invention relates to an optical disk reproducing apparatus for reproducing information recorded on an optical disk and, in particular, relates to an optical disk reproducing apparatus also capable of reproducing information recorded on an optical disk of a hybrid type formed by a CD (Compact Disc) layer and an HD (Hi-Definition) layer.
2. Description of the Related Art
In recent years, a DVD (Digital Versatile Disc) which is a new optical disk having a larger capacity than a CD has been spread. In the DVD, information is recorded on an optical disk having a diameter of 12 cm at a track pitch of 0.8 μm which is a half of the track pitch of 1.6 μm employed in the conventional CD, the wavelength of a semiconductor laser is changed from 780 nm for the CD to 630 nm for the DVD, and the EFM (Eight-to-Fourteen Modulation) adopted for the CD is improved to consequently realize high-density recording which corresponds to information of approximately 4 G bytes on one side of the disk. In such a DVD, an optical disk of a hybrid type having two layers as recording layers has been spread.
When such an optical disk of a hybrid type is an SACD (Super Audio CD), a 16-bit digital audio signal sampled at a frequency of 44.1 kHz, for example, is recorded on one of the layers, that is, a CD layer, while a 1-bit digital audio signal being processed through the SIGMA DELTA modulation at a frequency of 2.842 MHz, for example is recorded on the other layer, that is, an HD layer. The HD layer is divided or partitioned into a two-channel area and a multi-channel area.
In the conventional optical disk reproducing apparatus also capable of reproducing information of such an SACD, when reproducing an SACD, at first an audio signal on the two-channel area of the HD layer is reproduced, then an audio signal on the multi-channel area of the HD layer is reproduced, and thereafter an audio signal on the CD layer is reproduced. That is, the specification for changing the reproducing area based on operations of keys is arranged to change the reproducing areas in an order of a two-channel area of the HD layer, a multi-channel area of the HD layer and an area of the CD layer.
At the time of reproducing information from an SACD, access list information of TOC (Table Of Contents) is required when converting time information into address information. The time information is information contained in the TOC information and represents a reproduction start time and a reproduction time period for each track. The address information is information contained in the TOC information and represents a reproduction start address and a reproduction sector number for each track. The access list information has different information for each of the two-channel and the multi-channel. The information for each of the two-channel and the multi-channel amounts to 65 K bytes.
For example, when three frames are constituted by fourteen sectors in the Direct Stream digital (DSD) format, based on the access list information, the conversion from the time information to the address information is attained in accordance with an expression of “address =(time information×14)/3”. Further, when three frames are constituted by sixteen sectors in the DSD format, based on the access list information, the conversion from the time information to the address information is attained in accordance with an expression of “address =(time information×16)/3”. In the Direct Stream Transfer (DST) format (flexible format), as the aforesaid expressions cannot be used, the access list is required.